Each string of a stringed musical instrument, such as a guitar, mandolin, violin, viola or cello, is attached at one end to the body of the instrument and extends under significant tension over a bridge, across the body, along an elongated neck and terminates at a headstock located at the end of the neck.
At the headstock, the other end of each string is wound around a respective capstan rotatably mounted on the headstock. The tension of each string, which determines its pitch of vibration, is individually adjustable by rotating the appropriate respective capstan.
In an arrangement often used on guitars and mandolins, the capstan is mounted with its rotational axis oriented perpendicularly to the plane of the headstock. A gear is coaxially mounted on the capstan. The gear engages a worm gear mounted on a shaft having an axis of rotation oriented perpendicularly to the axis of the capstan. The shaft extends outwardly from the headstock and has a tuning button affixed to its end, the tuning button providing purchase to manually turn the shaft. When the shaft is turned, the worm gear turns the gear on the capstan, thereby turning the capstan and adjusting the tension of the particular string attached to it.
The gear ratio between the worm gear and the capstan gear is typically on the order of 16 to 1, meaning that the shaft must be rotated through 16 complete revolutions to effect one full revolution of the capstan. This gear ratio is advantageous when fine tuning a string to a precise pitch because it allows small adjustments in string tension to be made with relatively large rotations of the shaft. However, the gear ratio presents a distinct disadvantage when changing a string on the instrument because the winding button must be turned many times to release the tension of the old string and then apply the required initial tension to the new string before it can be fine tuned to the precise pitch desired.
When changing a string, musicians often use a simple crank device to help them turn the winding button to release the tension of the old string and apply the initial tension to the new string. The crank has a cup at one end which engages the tuning button and a handle extending perpendicularly to the cup and offset from its center. The handle is held between the fingers and thumb of the hand and rotated rapidly by wrist action to turn the winding button and release the tension on the old string or apply the initial tension to the new string. Once the tension of the new string is near the desired value, the crank is disengaged and the tuning button is turned manually to achieve the desired pitch.
There are two problems with the simple crank device. First, the cup tends to wobble as it is turned, bringing the outside edges of the cup in grazing contact with the headstock of the instrument, often leaving unsightly score marks which can adversely affect the resale value of the instrument.
Second, operation of the crank is tiring and stressful to the wrist of the user and can lead to repeated motion injury such as carpal tunnel syndrome or the formation of ganglionic cysts.
Both of these problems are related to the fact that the simple crank is turned using the wrist and the relatively small muscles which control its flexing. The turning motion generated by circularly flexing the wrist joint does not orbit about a single true axis but precesses in a cone of revolution about a central axis. This can be observed by holding a pencil between the index finger and thumb and rotating the pencil in a circle by means of wrist motion alone. The tip of the pencil describes a cone. In the simple crank, the cup is eccentrically mounted at the end of the crank handle, and when the handle is turned by the wrist, the cup naturally wobbles toward and away from the headstock as it traverses the conical path described by the end of the handle.
The natural wobble is exaggerated as the wrist muscles grow tired. These muscles tend to fatigue quickly which leads to a loss of control of the simple crank. For many musicians, the wrist muscles cannot keep adequate control of the crank for the number of turns required to tension the string and the wobble of the cup increases.
Finally, it is well known that the wrist is a complex joint through which nerve ganglia, tendons and blood vessels must pass while allowing the full range of motion to the hand. The complexity makes the wrist especially vulnerable to repeated motion trauma and not ideally suited to operate a crank.
Changing a string also typically requires that the string be trimmed to length. When a new string is mounted on an instrument and tuned to the desired pitch, there is often a relatively long extraneous piece of the string protruding from the capstan. It is preferable to cut this protruding piece so that it will not rattle and produce noise when the instrument is played. The practice has been to cut the string with a pair of wire snips. There are several disadvantages to this solution however. The blades of the wire snips tend to leave a hook-like deformation on the string end which tends to snare clothing and will also inflict painful injury to the skin of a person coming in contact with the end. Furthermore, wire snips tend to have exposed steel parts which will damage the instrument if they come into contact with it, as, for example, when the wire snips are stored in the instrument's case and become loose when the case is in transit.
There is clearly a need for a better device useable by musicians to perform the tasks, such as string winding and trimming, associated with changing the strings of instruments such as guitars and the like, which does not suffer from the disadvantages outlined above.